1. Field of the Invention
The invention relates generally to furnaces, particularly electric arc furnaces and, more particularly, to a method and apparatus for installing or replacing a furnace tap hole insert.
2. Description of the Currently Available Technology
In conventional furnaces, such as EBT or electric bottom tap arc furnaces, molten metal from the furnace is removed through a tap hole formed in a well block at the bottom of the furnace. The well block is made of refractory material and has a well block channel formed therein. A plurality of stacked, annularly-shaped tap hole insert pieces are placed in the well block channel to form a tap hole insert, with the central openings of the insert pieces aligned to form a tap hole passage in the bottom of the furnace. The tap hole passage defines the flow path of molten metal out of the furnace. The insert pieces are typically formed of refractory material. The stacked tap hole insert pieces are held in position in the well block channel by bonding material, such as conventional xe2x80x9cdry vibexe2x80x9d material, which is poured into the gap formed between the sides of the insert pieces and the side of the well block channel. The insert pieces are also supported by a retaining piece attached to the bottom of the furnace to help prevent the insert pieces from dropping out of the bottom of the well block channel during use. For example, the retaining piece may have slots or holes, which are configured to engage lugs on the bottom of the furnace.
Molten metal from the furnace flows through the tap hole passage formed by the aligned tap hole insert pieces and out of the bottom of the furnace. With time, the insert material begins to burn away due to the passage of the molten metal, which increases the inside diameter of the tap hole passage. When the annular width of the insert material decreases to a certain predetermined point, the insert must be replaced.
In a currently practiced method of replacing the tap hole insert, the retaining piece is unfastened from the bottom of the furnace and is lowered or dropped onto the floor below the furnace. A hollow metal tower or cage is lowered into the furnace. The metal tower has an opening at the bottom, which is slightly larger than the outside diameter of the tap hole insert. The tower is lowered into the furnace until the bottom hole of the tower is adjacent the top of the tap hole insert. A worker climbs into the tower and descends with a hand-held jackhammer to the bottom of the tower. The worker then uses the jackhammer to knock out and chip away the old tap hole insert and associated bonding material. After the tap hole insert is chipped away, a cable is dropped by a crane through the top of the tower and is guided by the worker inside the tower through the well block channel and out of the bottom of the furnace. The cable has an engagement element, such as a metal bar, located at the end of the cable. This engagement element and cable are threaded through a group of replacement insert pieces located on the floor under the furnace. The crane then retracts the cable, pulling the insert pieces into the well block channel to replace the old tap hole insert. The retaining piece is reattached to the bottom of the furnace and dry vibe bonding material is poured into the top of the furnace. The bonding material flows into the gap between the outside of the tap hole insert and the inside of the well block channel to help retain and seal the tap hole insert in place until the insert must again be replaced. The tower and cable are withdrawn from the furnace.
There are drawbacks associated with this conventional method of replacing the tap hole insert. For example, this conventional method requires a worker to enter a tower temporarily positioned inside of the hot furnace. This poses a safety risk for the worker involved. Additionally, this conventional method is very time-consuming and detrimentally impacts upon the productivity time for the furnace. Therefore, it would be advantageous to provide a method and apparatus for installing or replacing a tap hole insert which reduces or eliminates at least some of the drawbacks of the currently practiced method.
The objects of the present invention are achieved with the apparatus for replacing a tap hole insert in a furnace according to the present invention. The apparatus of the present invention includes a drill detachably mounted to a drive shaft in a boom arm of a utility machine with the drill adapted to remove the existing tap hole inserts to be replaced from outside of the furnace interior, and a tap hole insert tool detachably mounted to the boom arm of the utility machine with the tap hole insert tool adapted to hold and insert tap hole inserts into the furnace tap hole from outside the furnace interior. The invention may include a conventional moving utility machine and an insert tool stand for supporting the tap hole inserts prior to positioning of the tap hole inserts onto the tap hole insert tool. In particular, the insert tool stand may include a base platform and a pair of adjustable side stanchions.
The drill may be a self-centering drill that includes a centering pilot cap at a forward end of the drill, the pilot cap formed as a cylindrical member substantially equal in diameter to the interior diameter of the existing tap hole inserts of the furnace whereby the pilot cap centers the drill during removal of existing tap hole inserts from the furnace. The drill may include a cylindrical base with a plurality of cutting teeth positioned at a forward end of the base, wherein each of the cutting teeth is a rotatable cutting insert positioned in a cutting insert body along a longitudinal axis, such that the positioning of the cutting faces of the inserts and the positioning longitudinal axes of the cutting inserts define a lacing pattern for the drill. The lacing pattern is defined by alternating adjacent inserts between having the longitudinal axis and the cutting faces of individual inserts face radially inwardly of the cylindrical body and having the longitudinal axis and the cutting faces of individual inserts face radially outwardly of the cylindrical body. The drill may include a socket at a rear end of the base that is adapted to be releasably attached to a drive shaft of the utility machine.
The tap hole insert tool may include a shaft receiving the tap hole inserts thereon, a first retention member at a first end of the shaft for preventing the tap hole inserts from moving along the shaft in a first direction beyond the first retention member and a second retention member removably positioned on the shaft for preventing the tap hole inserts from moving along the shaft in a second direction beyond the second retention member. The first retention member may be formed as a stepped flange and the second retention member may be formed as a removable pin.
The method of replacing tap hole inserts from a furnace according to the present invention includes the steps of: attaching a drill to a utility machine; drilling the existing tap hole inserts to be replaced from outside of the furnace interior with the drill to remove the existing tap hole inserts; removing the drill from the utility machine; attaching a tap hole insert tool to the utility machine; positioning the replacement tap hole inserts onto the tap hole insert tool; inserting the tap hole insert tool and the tap hole inserts into the furnace tap hole from outside the furnace interior; bonding the tap hole inserts to the tap hole; and removing the tap hole insert tool from the tap hole.
These and other advantages of the present invention will be clarified in the description of the preferred embodiments taken together with the attached figures wherein like reference numeral represent like elements throughout.